1. Field of the Invention
This invention relates to solid state devices and circuits and particularly to solid state devices and circuits capable of handling relatively large amounts of power. Most particularly, this invention relates to a new and improved method and apparatus for mounting a solid state device or circuit to heat dissipation plate such as ground plane for greatly increasing the amount of heat dissipation achieved to thereby render the device or circuit capable of handling increased amounts of power.
2. The Prior Art
Heretofore, to increase the heat dissipation of solid state devices and circuits, it has been known to affix to the bottom of a heat conductive substrate supporting the device or circuit a metal stud which serves as a heat sink. Generally, the stud is connected to a metal plate underlying the conductive ceramic and the plate is connected to the conductive ceramic substrate as by an epoxy glue or solder. Both the metal plate and the metal stud are included to dissipate heat generated in the conductive or semi-conductive film on the ceramic substrate. Such devices have not been overly efficient principally because, interposed between the metal base plate and the conductive ceramic is a layer of so-called thermally conductive epoxy glue or solder which is in fact, notwithstanding the thinness of the layer, substantially resistant to thermal conduction. Thus, the layer greatly reduces the heat dissipation. Similar problems may also be encountered between the metal plate and the metal stud depending therefrom.
A good discussion of the prior art and of certain so-called improvements thereto may be found in U.S. Pat. No. 3,513,362 granted to Isamu Yamamoto on May 19, 1970. In said Yamamoto patent, three varieties of prior art arrangements for improving the heat dissipation of semi-conductive devices are illustrated and then Yamamoto in FIGS. 4 through 6 of said patent illustrates three embodiments at his improvements over the prior art. The prior art shown in FIGS. 1 through 3 of the Yamamoto patent all show a solid state device 10 connected in some manner or other to an end portion which, in FIGS. 1 and 2 of Yamamoto, are of smaller cross section and which in FIG. 3 is of greater diameter and are respectively designated by the reference characters 12' and 22. In each of the assemblies shown in FIGS. 1 through 3, the heat to be dissipated is generated in the semiconductive device 10, the heat being dissipated principally through the end portions 12 and 22. However, it will be obvious that the end portions 12 and 22 are secured to the semi-conductive device 10 in the typical manner heretofore known, namely, by a suitable adhesive or solder which in the past has significantly reduced the capability of such assemblies to dissipate large amounts of heat energy. It is for that reason that none of the prior art arrangements shown in FIGS. 1 through 3 of Yamamoto have been altogether successful in solving have problem of heat dissipation. Thus, the power rating of devices and circuits using the teachings of FIGS. 1 to 3 have been sharply limited. from the ceramic plate to the support block. To dissipate heat from the support block, the 16.
Similarly, in FIGS. 4 to 6 of Yamamoto, Yamamoto's solution to the prior art problems is shown. In Yamamoto, the semiconductor device is mounted on a ceramic substrate which in turn is affixed to a circular support block. While Yamamoto does not expressly disclose the manner in which the substrate is connected to the support block, it is apparent that he could only hve done this in the manner of the prior art, namely, by an intervening adhesive or solder layer which greatly interferes with the conduction of heat from the support block, the block is secured to an underlying heat dissipation plate 16 by a clamp welded to the plate 26. However, heat generated in the semiconductor device 10 must still get into the support block 22 and this requires it to pass through the insulating layer of epoxy or solder. Thus, it remains difficult to dissipate heat generated in the semiconductor 10.